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Tuna

28 August 2012

Iain Angus, skipper of Lochlan (Seatrek), reported sightings of Tuna on his trip over to St Kilda last week!  Here's a first hand description:

"The main shoal was 9 miles to the north east of Boreray , we saw an unusually large and concentrated flock of diving gannets which were accompanied by a few fulmars, skuas, Manx shearwaters, sooty shearwaters, black back gulls and herring gulls.  We went over to investigate fully expecting to find the usual dolphins feeding on a shoal of herring.  I told the passengers to get their cameras ready for the spectacle of diving birds and jumping dolphins and probably minke whales too.

The leading edge of the diving gannets was unusually fast moving at 5 knots and as we closed to 20m we could see the fast moving splashes among them and we were amazed to see the characteristic upright thin forked tails of tuna darting through the water. We managed to get within 10m of them and could see they were about 6/7 ft long, maybe more, so were possibly bluefin.  The next shoal was at 6.5 miles from Boreray  and this one was moving much faster say 10 knots to the south west and zigzagging with birds showing their whereabouts when near the surface, the fish were about the same size.  The most distinctive sight of the whole thing was just how many gannets were following them, I have never seen such a flock in such a small area so they could be seen from miles away."

 


That was a surprise to me but Angus (Kilda Cruises) provided some very useful and interesting links where I learnt this...  

"Bluefin tuna has been over-fished in the last twenty years but some recent studies and climatic changes are showing an encouraging rebirth of the North Atlantic population thanks to some great conservation efforts in the Western Atlantic (Blue fin tuna - Garmin & Airmar). 

Bluefin tuna could be present in an area and never be seen on the surface if there was enough food for them deep in the water. Tuna isn’t a properly warm blooded animal but it can keep its body several degrees warmer than the surrounding water thanks to a sophisticated blood system. But, to do that, they need to burn energy coming from fat-rich fish like herring, sardines and mackerel.  They need to maintain a 77°F body temperature and therefore need to eat all day long when not migrating.  Going to extreme latitude where food is plentiful often takes them to extreme conditions as is the case in NW Scotland. There are reports of large Bluefin tuna feeding in places like the Faeroes islands, way up north... Airmar technology has launched a summer fishing expedition focusing on using the latest technology to locate Atlantic bluefin tuna in the waters surrounding Scotland. ” (extracted from Airmar expedition blog: Bluefin tuna - past and present)


Many of the passengers aboard 'Lochlan' were taking photographs - if I can get hold of any images then I'll make sure to post them here...  (if you were a passenger that day, please get in touch!!)

Gina


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